The buildings of Kazuyo Sejima are among the most emphatically beautiful in recent years. Working solo or in collaboration with Ryue Nishizawa, Sejima’s eye for the ethereal and delicate has resulted in wafer-thin structures that appear to defy gravity, climate and the mess of everyday life. They instigate games of transparency and porosity, reflectivity and refraction both on tight urban lots (Sejima’s Small House on a cul-de-sac in Aoyama, Tokyo, 2000) and in more pastoral settings in provincial Japan (the critically acclaimed 21st Century Museum of Contemporary Art, Kanazawa, 2004). Sejima + Nishizawa and Associates (SANAA) is now building across Europe - Essen, Almere, Valencia, Basel - and in the United States. In Lower Manhattan, SANAA’s proposal for the New Museum of Contemporary Art, a small tower of stacked boxes, is under construction on the Bowery east of SoHo. But the Japanese duo’s first completed American building is in the comparatively minor city of Toledo, Ohio. It’s a pavilion for the display of a remarkable collection of glass objects and the accommodation of glass-blowing studios, most of which is ingeniously made visible to public view. The walls of the Glass Pavilion are made almost entirely of glass. Floor-to-ceiling panels of glass connect the floor plate and the miraculously thin white parapet above into one flush, contiguous surface. There are no obtrusive mullions to jar the illusion of transparency and a floating roof. And corners curve in plan so that the figure of the building is never fixed. It soon becomes apparent that there are further walls of glass within the glazed perimeter, boxes or volumes of light hovering inside this world that seems caught between solidity and a state of fluidity - a nimble allusion to the nature of glass itself. The pavilion is found across a broad street from its mother institution, the Toledo Museum of Art, a neo-classical edifice from the early 20th century set off by a grand flight of steps and a tall Ionic colonnade. In 1993, Frank Gehry added a fractured yet elegant building to the southeast end of the museum; clad in lead-covered copper and glass, it houses the University of Toledo’s Center for the Visual Arts. Thus SANAA’s project, while freestanding, is the latest component in this campus of museum and educational buildings. It is on an oblong lot planted with mature oaks and maples. As with many of the practice’s buildings in Japan, the radically slim tectonics of SANAA’s Glass Pavilion benefit from the proximity of nature (in this respect, the Almere Kunstlinie Theatre and Cultural Centre in The Netherlands seems relatively dull and grey). In Toledo, in summer, the foliage of the trees adds colour and shelter and is, furthermore, reflected in the new glass walls such that the building appears almost kaleidoscopic. In winter, the trees are reduced to skinny trunks and branches amid the snow; reflections in the pavilion’s glass walls appear like ghostly tattoos. In all seasons, a path through the trees continues to wind its way through the pavilion. This serpentine corridor connects a lobby facing south towards the main museum building with a second entrance close to a surface car park to the east. In-between, along the internal path, the so-called “crystal corridor” functions as a central organizing device. From there, visitors can look directly into the first of two hot shops with its array of blazing furnaces, see the display of both old and contemporary glass in several discrete galleries, or glimpse patches of sky caught by courtyards embedded within the pavilion’s taut form. The building sits on the ground, allowing for ease of transition between exterior and interior. In this regard, it is more like Philip Johnson’s Glass House in New Canaan, Connecticut (1949) than Mies van der Rohe’s Farnsworth House in Plano, Illinois (1951). Whereas both those American classics are rectilinear, the Glass Pavilion has rounded corners. If the Glass House has a single cylindrical brick core, the Glass Pavilion contains a myriad small pavilions, all with rounded corners and most made of glass panels like the outer membrane. The resulting plan is a set of enclosed rooms and patios separated by labyrinthine corridors between the glass walls. Thin white gauze and heavier pale grey curtains occupy these in-between zones and help shade the interior. Visitors move from one chamber to the next by piercing the double walls via orthogonal glazed links. With low iron content to facilitate transparency, the glass was made in Germany yet fabricated into eight-foot-wide panels in China. The pale grey/beige terrazzo floor flows unimpeded throughout, as does the white ceiling where necessary services are gathered in discreet tracks. The ensemble suggests both the rational and the organic, the simple and complex. How does this delicately seductive structure stand up? Whereas one opaque room - the lampworking studio - has thin walls of rolled steel, and whereas few freestanding walls house cross-bracing elements, the primary support is provided by three dozen cylindrical steel columns that are also white and that again almost disappear (the more observant visitor may associate these skinny verticals with the trunks of trees outside). The freestanding walls also house air supply, fire-fighting and intercom equipment with circular vents that recall, in their conflation of technology and Pop iconography, utopian aspects of the 1960s. A basement contains workshop and storage rooms. One circular glass disk allows a small splash of light from an inner patio to the lower floor. Down there, double doors are inset with porthole windows in accordance with the project’s circular motif. As in many neo-classical buildings, the basement has technical plant to service the pavilion above: hot air from the glass-blowing studio is both expelled through its roof and drawn down to be re-circulated through the floor slab. Between the pavilion’s inner and outer glass walls, the interstitial space - a kind of exposed poche - works to mediate differences in temperature between the galleries and the outside air. In Toledo, a city with great industrial and artistic glass traditions, the museum presented its architects with a brief uncannily appropriate to their progressive aesthetics. Sejima and Nishizawa have responded with a building that verges on perfection.